How do I satisfy a warning for casting a collection in java/jsp

Question

In my JSP I get a warning for this cast

<%
  Collection<Server> svr = (Collection<Server>)request.getAttribute("serverCollection");
%>

instanceOf doesn't seem to work here

Multiple annotations found at this line: - Type safety: Unchecked cast from Object to Collection - Type safety: Unchecked cast from Object to Collection — stackoverflow, Jun 29 '11 at 13:38
Should I suppress or try to fix the problem? Is this an inherent problem/warning for this type of utilization? — stackoverflow, Jun 29 '11 at 13:40

score 3 · Accepted Answer · edited May 23 '17 at 12:19

3

<%
    @SupressWarnings("unchecked")
    Collection<Server> svr = (Collection<Server>)request.getAttribute("serverCollection");
%>

BTW, using scriplets is not very good thing, read this thread about avoiding scriplets.

edited May 23 '17 at 12:19

Community

1
1

answered Jun 29 '11 at 13:42

Roman

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score 1 · Answer 2 · answered Jun 29 '11 at 13:40

You can't "satisfy" that warning. It is an unchecked cast, and you can't really do anything about it since the method returns an Object.

If you're absolutely positive the attribute will always contain a Collection<Server> you can add a @SuppressWarnings("unchecked") annotation.

score 1 · Answer 3 · answered Jun 29 '11 at 13:45

1

You could use JSTL instead of scriptlets. It would look like:

<c:set var="svr" value="${requestScope['serverCollection']}"/>

answered Jun 29 '11 at 13:45

Nathan Hughes

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@Marshll187: it would go in the same place. – Nathan Hughes Jun 29 '11 at 13:48

score 0 · Answer 4 · answered Jun 29 '11 at 13:48

You cannot avoid this warning (except by suppressing it). The problem is that Java at runtime is only able to check that the object is of type Collection at runtime when casting. It cannot check that it is of type Collection<Server>. That is what the error means.

How do I satisfy a warning for casting a collection in java/jsp

4 Answers4